This invention relates in general to an endless metal belt assembly, and in particular to an endless metal belt assembly which is formed in accordance with specific belt and lubricant relationships in order to maximize load sharing capability and to minimize total stress.
Endless metal belts have many uses, including their use as drive members for continuously-variable transmissions. When used in this manner, an endless metal belt assembly must have certain properties and characteristics to operate efficiently.
The endless metal belt should be strong, exhibiting both high fatigue strength which reduces the likelihood of failure from fatigue fracturing, and high compressive and tensile strength which enables the belt to withstand the demands imposed by the bending stresses inherent in the operation of the dual pulley system of the continuously-variable transmission. The belt should be able to stretch without yielding and be flexible. It should be durable with high wear resistance, because replacement is costly and takes the transmission out of use. The belt material should have high processability and be capable of being fashioned into a very thin layer which can be manufactured to a highly precise circumferential length. In the event of multiple belts forming a continuously-variable transmission belt assembly, this high precision of circumferential length for each successive belt is especially critical to the formation of uniform gaps between adjacent belts. The multilayered belt assembly should have exacting tolerances with respect to the distance between belts. The adjacent surfaces of the belts should be conducive to maintaining a lubricated state between the belts. Each belt of a belt assembly should be capable of equal load sharing. The outer surface of the belt assembly should have sufficient friction to transfer the load from the driving pulley to the driven pulley.
Van Doorne U.S. Pat. No. 3,604,283 discloses a flexible endless member consisting of one or more layers of steel belts for use with a continuously-variable transmission, containing a driving mechanism which comprises a driving pulley with a V-shaped circumferential groove and a driven pulley with a V-shaped circumferential groove. The flexible endless member, which has chamfered (beveled) flanks, interconnects and spans the pulleys, and the diameters of the pulleys automatically and steplessly can be varied with regard to each other in such a way that different transmission ratios can be obtained. The steel belts forming the driving mechanism of this invention are arranged with a mutual play ranging from 0.3 to 1.8.times.the thickness of the belt.
Cuypers U.S. Pat. No. 4,661,089 discloses an endless metal belt for use with a continuously-variable transmission which incorporates permanent compressive stresses in the belt's edge zones by a ball peening or rolling treatment. The belt is configured so that the thickness of the belt edge zones decreases toward the longitudinal belt edges. By reducing the stresses in the edge zones, in particular the tensile stresses caused by the bending stress, the strain on the belt is not so great, and the likelihood of belt breakage caused by hairline cracks occurring from the edges is decreased.
Endless metal belts used for belt drives can be formed by several methods. One manufacturing method disclosed in Metals Handbook, 9th, ed. employs a "ring rolling method" wherein a metal, cylindrical tube is cut to a specified length and then an innermost belt is formed on the ring-rolling machine, making the ring wall thinner and the circumferential length longer. A number of additional belts, wherein the radius of each belt is slightly larger than that of the previously formed belt, can be similarly formed. The belts are then subjected to solution annealing in a vacuum furnace on a stainless steel cylinder, where the layered belts are rotated around two pulleys with tension in order to adjust the gap between the belts. After the dimensional correction, the layered belt is processed by precipitation-hardening (e.g., 490.degree. C. for 3 hours) and surface-nitriding. Finally, in order to improve lubrication ability between belts, surface profiling is performed.
Rush U.S. Pat. No. 4,787,961 discloses a method of preparing multilayered endless metal belts, wherein tensile band sets are formed from a plurality of separate looped endless bands in a nested and superimposed relation. The bands are stated to be free to move relative to each other, even though the spacing between the adjacent lands is relatively small. At least one band is formed by an electroforming process.
When endless metal belts are used with a continuously-variable transmission, they are exposed to the many stresses inherent in a continuously-variable transmission. It is therefore desirable to minimize these stresses in order to maximize the load-carrying capability of the belt. It is also desirable to have a lubricating film between adjacent belts which will transmit torque as well as prevent slippage of the belts and overall loss of the transmission's load-carrying capability.